#include "tss.h"
#include "stdint.h"
#include "thread.h"
#include "global.h"
#include "print.h"
#include "string.h"


struct tss {
    uint32_t backlink;
    uint32_t* esp0;
    uint32_t ss0;
    uint32_t* esp1;
    uint32_t ss1;
    uint32_t* esp2;
    uint32_t ss2;
    uint32_t cr3;
    uint32_t (*eip)();
    uint32_t eflags;
    uint32_t eax;
    uint32_t ecx;
    uint32_t edx;
    uint32_t ebx;
    uint32_t esp;
    uint32_t ebp;
    uint32_t esi;
    uint32_t edi;
    uint32_t es;
    uint32_t cs;
    uint32_t ss;
    uint32_t ds;
    uint32_t fs;
    uint32_t gs;
    uint32_t ldt;
    uint32_t trace;
    uint32_t io_base;
};

static struct tss tss;

void update_tss_esp(struct task_struct* pthread){
    tss.esp0 = (uint32_t*) ((uint32_t)pthread + PG_SIZE); 
}

static struct gdt_desc make_gdt_desc(uint32_t* desc_addr, uint32_t limit, uint8_t attr_low, uint8_t attr_high){
    uint32_t desc_base = (uint32_t)desc_addr;
    struct gdt_desc desc;
    desc.limit_low_word = limit & 0x0000ffff;
    desc.base_low_word = desc_base & 0x0000ffff;
    desc.base_mid_byte = ((desc_base & 0x00ff0000) >> 16);
    desc.attr_low_byte = (uint8_t) attr_low;
    desc.limit_high_attr_byte = ((limit & 0x000f0000)>>16) + (uint8_t)attr_high;
    desc.base_high_byte = desc_base >> 24;
    return desc;
}

void tss_init(){
    put_str("tss_init start\n");
    uint32_t tss_size = sizeof(tss);
    memset(&tss, 0, tss_size);
    tss.ss0 = SELECTOR_K_STACK;
    tss.io_base = tss_size;

    *((struct gdt_desc*)0xc0000920) = make_gdt_desc((uint32_t*)&tss, tss_size - 1, TSS_ATTR_LOW, TSS_ATTR_HIGH);
    *((struct gdt_desc*)0xc0000928) = make_gdt_desc((uint32_t*)0, 0xfffff, GDT_CODE_ATTR_LOW_DPL3, GDT_ATTR_HIGH);
    *((struct gdt_desc*)0xc0000930) = make_gdt_desc((uint32_t*)0, 0xfffff, GDT_DATA_ATTR_LOW_DPL3, GDT_ATTR_HIGH);

    uint64_t gdt_operand = (8*7-1) | ((uint64_t)(uint32_t)0xc0000900 << 16);
    
    asm volatile ("lgdt %0" :: "m"(gdt_operand)  );
    asm volatile ("ltr %w0" :: "r"(SELECTOR_TSS) );
    put_str("tss_init & ltr done\n");
}


































